Groundwater Potential Assessment and Characterization of Genale-Dawa River Basin
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AAIT Groundwater potential assessment and characterization of Genale-Dawa River basin By: Nebiyou Kassahun 2015 [Type text] I D N O GSR/2651/06 ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES FACULITY OF TECHNOLOGY Groundwater potential Assesment and Characterization of Genale- Dawa river basin A thesis submitted to the School of Graduate Studies of Addis Ababa University in partial fulfillment of the Degree of Masters of Science in Civil Engineering (Stream: Hydraulic Engineering) By Nebiyou kassahun Approval by Board of Examiners ---------------------------------------------------- ------------------ Chairman (department of graduate committee) Signature Dr.-Ing Mebruk Mohammed . Advisor Signature Dr. Agizew Nigussie . Internal Examiner Signature Dr.-Ing. Asie Kemal Jabir . External Examiner Signature Groundwater potential assessment and characterization of Genale-Dawa River basin Abstract Genale-Dawa River Basin is one of the largest basins in Ethiopia. It is one of the most drought prone regions in Ethiopia. As a result a search for alternative source of water has always been a major issue in the region. This study therefore, aims at characterizing and evaluating the ground water potential resource of Genale-Dawa basin. The results of this research ultimately contribute to development of better water resources potential management. Delineation of the Genale-Dawa River basin was carried out first in order to define the problem domain of the model. This has resulted in 17860km2 area of the basin. This area was discretized to form a three dimensional. The discretized region has 19620 nodes, 17862 equilateral triangular elements of varying sizes with a maximum of 5km edge dimension and 2500km model thickness. The conceptualization of the model was done by grouping the discretized region in to 56 geological classes based on previous geological survey of the basin. The equivalent porous medium modeling approach was used to represent the different geological classes in the basin. Moreover, 23 rain gauge stations were used to determine the areal precipitation over the basin. The model takes perennial rivers as constant head boundaries, the side and bottom geometric boundaries of the model as no flow boundaries and the recharge due to precipitation as specified flow boundary. After conceptualization of the flow system was complete and numerical model developed, TAGSAC model manual calibration was done by seating hydraulic conductivity and percentage recharge as calibration parameters when calibration is complete. The result was evaluated quantitatively using average indicators (AM, RMS, MAE) and qualitatively by comparison of groundwater contour maps generated with recorded and simulated hydraulic head data. The calibration model was then used to determine monthly groundwater table fluctuation which eventually enabled the estimation of groundwater recharge potential of the basin. Additionally, base flow separation of perennial rivers was done to determine the monthly excess flux from the aquifer system. By adding these two values the total replenishable groundwater was estimated to be 2.78BMC. Hydro-geological map was also prepared based on hydraulic conductivity values obtained from model calibration. Identification of major groundwater recharge and discharge areas have also been done as an attempt towards basic groundwater flow system characterization. By Nebiyou k. Page ii Groundwater potential assessment and characterization of Genale-Dawa River basin Key words: Ethiopia; Genale Dawa River Basin; Numerical Groundwater modeling; Replenishable Groundwater Potential; TAGSAC By Nebiyou k. Page iii Groundwater potential assessment and characterization of Genale-Dawa River basin Acknowledgment First, I would like thank Debremarkos University for granting me the scholarship to study in Addis Ababa University and giving me a paid leave of absence during the time of my study and research. Most of all, my greatest appreciation goes to my advisor, Dr. Mebruk Mohammed, who invested his time, knowledge and energy throughout the whole research work. He is very supportive, willing, and hard working; in generally he has been an inspiration to me professionally. My deepest gratitude also goes to my family members who has encouraged me and supported me in ideas to the completion of my work. Furthermore, I would also like to express my warmest gratitude to Water Works Design and Supervision Enterprise, Ethiopian Ministry of Water Resources and Energy, and National Metrological Agency for their collaboration during secondary data collection. Lastly I want to thank friends, who encouraged and supported me to finish this research. By Nebiyou k. Page iv Groundwater potential assessment and characterization of Genale-Dawa River basin Table of Contents Abstract .................................................................................................. ii Acknowledgment ................................................................................... iv Table of Contents .................................................................................... v List of Figures and Tables ..................................................................... viii 1. Introduction .................................................................................... 1 1.1. Statement of the problem ............................................................ 2 1.2. Objective of the study .................................................................. 2 1.2.1. Specific objectives ................................................................... 3 2. Literature review ............................................................................. 4 2.1. Description of the area................................................................. 4 2.2. Hydrology and Climate ................................................................. 2 2.3. Geology ........................................................................................ 5 2.4. Previous work .............................................................................. 6 2.5. Groundwater flow Model formulation ......................................... 8 2.5.1. Physical model ........................................................................ 8 2.5.2. Analog models ........................................................................ 8 2.5.3. Mathematical models ............................................................. 9 2.5.3.1. Governing equations for saturated ground water flow ...... 10 2.5.4. Analytical modeling .............................................................. 15 2.5.5. Numerical modeling ............................................................. 15 By Nebiyou k. Page v Groundwater potential assessment and characterization of Genale-Dawa River basin 2.5.5.1. Finite-difference method (FDM) ........................................ 16 2.5.5.2. Finite-element method (FEM) ............................................ 19 3. Methodology ................................................................................. 25 3.1. Data collection ......................................................................... 25 3.2. Numerical solution technique ................................................. 26 3.3. Spatial discretization ............................................................... 27 3.4. Conceptual model ................................................................... 30 3.5. Model calibration .................................................................... 33 3.6. Estimation of Groundwater potential ...................................... 36 4. Results and discussion................................................................... 38 4.1. Water point inventory data ..................................................... 38 4.2. Rainfall distribution ................................................................. 39 4.3. Base flow separation ............................................................... 41 4.4. Flow system boundary ............................................................ 43 4.5. Model calibration .................................................................... 44 5. Conclusion and Recommendation ................................................ 56 5.1. Conclusion ............................................................................... 56 5.2. Recommendation .................................................................... 57 Reference .............................................................................................. 58 Appendix 1 ............................................................................................ 61 Continuous Base flow Separation Method ............................................ 61 Appendix 2 ............................................................................................ 62 Water point calibration data ................................................................. 62 By Nebiyou k. Page vi Groundwater potential assessment and characterization of Genale-Dawa River basin Appendix 3 ............................................................................................ 70 Geological coding .................................................................................. 70 Appendix 4 ............................................................................................ 72 Mat lab Code for filling missing rainfall data ........................................ 72 By Nebiyou k. Page vii Groundwater potential assessment and characterization